Antenna supply phase and amplitude control



Sept., M, 1948. w. J. OBRIEN ANTENNA SUPPLY PHASE AND AMPLITUDE CONTROL 2 Sheets-Sheet l Filed April 13, 1942 /MW @i MMM/VUT @Ef/A4 INVENTOR r OAWL-'n ANTENNA SUPPLY PHASE AND AMPLITUDE CONTROL Filed April 15, 1942 2 Sheets-Sheet 2 zza fw@ 2?/ wp ,205

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Pif/20AM U. OER/EM INVENTOR tennae is equal.

Patented Sept. 14, 1948 TEN?? ENCE ANTENNA SUPPLY PHASE AN D AMPLITUDE CONTROL William J. OBrien, Los Angeles, Calif., assgnor to The Deccal Record Company, Limited, London, England, alcorporation of Great Britain Application April 13, 1942, Serial No. 438,712

(Cl. Z50-17) 7 Claims. 1

My invention relates to a radio frequency transmission system and has particular reference to a radio frequency transmission system particularly adapted for use in connection with radio beacon systems such as are employed as an aid in the navigation vof aircraft or other mobile vehicles.

The radio beacon systems which are in current use today are of the type referred to as the equisignal type. These systems employ a plurality of spaced radio frequency transmitting antennae which are so excited as to produce in space an equi-potential electrical surface, which surface is used as an aid to the navigation of aircraft. Such a system serves to define a. course extended toward a desired objective or destination, which course comprises the locusl of all points at which the intensity of the signals received from each of the plurality of radio frequency transmitting an- 'Ihe signals are normally rendered distinguishable either by modulating each of the pair of signals at dierent audible frequencies or by distinguishably keying the transmitting antennae. The on course position ofa vehicle is in-dicated by the reception of equal signals, whereas, the olf course location of the `vehicle is indicated by the reception of signals in which one signal predominates .over the other.

Considerable diiculty has been experienced in the use and operation of the equi-signal type of radio beacon `'system resulting from a tendency of the so-called beam or on course line defined by the system to wander or cscillate from side to side rthrough a considerable angle. The causes of the number of commercial airline crashes in the past have been directly traced to the wandering or wavering of the beacon beam. Investigation has shown that this wavering or wandering of the beam is produced by changesin the relative phase of the two radio frequency signals employed to produce the guiding surface. It has been found that a relatively slight shift in phase of one signal with respect to the other will produce a substantial shift in the compass direction of the course defined by the system.

f The causes of the phase changes which produce this wavering of the beam are principally changes in the transmitting antenna characteristics. Among the characteristics which have been found to be variable are the length of the antenna proper. It has been found that the actual physical length of the antenna will change as a result of changes in temperature and that there is also produced a still further change in the effective electrical length of the antenna due to changes occurring in the electrical circuits and also due.

to a change in the level of the electrical ground plane due to varying weather conditions, it being realized that the electrical ground plane does not necessarily coincide with the ground surface but usually lies some distance below the actual surface of the ground.

It has also lbeen found that the resistance of the antenna changes from time to time as a result of variation-s of the di-electric'constant yof the air which is in turn variable with' the variable weather conditions. Likewise the resistance of the antenna circuit varies with changes in ground resistance resulting from changing moisture content and changing salt content.- vApparent changes in the length and resistance of the antenna may also result from actual physical movement of the antenna as occurs, for example, duringa'storm. y

In my copending application Serial No. 420,059, led November 22, 1941, now abandoned, and entitle-d Radio beacon system, I have described and claimed a new and different type of radio beacon system fwhich differs from the conventional equi-signal system in that signals of different but harmonically related frequencies are continually radiated and the course which is dened by the system is the locus of points of a selected fixed multiple phase relation between the two sets of radiofrequency'signals. This=system is, of course, also sensitive to changes in the relative phase of the signals emanated from the transmitting antennae and While the System disclosed in my above-identified application is capable of providing an extremely high sensitivity and accuracy of course indication, this accuracy is nevertheless dependent, like that of the equisignaliype of systems, upon maintaining a constant phase relation between the various sets of signals emanated from-the radio beacon transmission antennae.

It is, therefore, an object of my invention to provide a novel radiofrequency transmission system which includes a control mechanism for maintaining fixed the phase of the transmitted signals,v

It is also an object of my invention to provide a system of the character set forth in the preceding para-graphs whichY includes a means for maintaining the antenna current constant irrespective of changes in the antenna characteristic-s.

It is an additional object of my inventionto provide -a systeml of .the character se't forth in the preceding paragraphs Which includes a means responsive to changes in radio frequency Voltage 28 thus operate to produce across the resistance 3|a direct potential which is directly proportional to the magnitude of the radio frequency current flowing in the antenna feeding circuit through the current transformer primary Windin'g 5. It will be noted that such direct potential as is produced across the resistance 3| will cause the conductor 32 tobe positive with respect to the conductor 33.

The control mechanism 21 also includes a second rectifier 31, the anode of which is connected as by means of a conductor 38 to a secondary winding 39 of a potential transformer 4D. The potential transformer 40 includes a primary winding 4| which is connected in shunt'I relation across the antenna feeder circuit, one terminal of the primary 4| being connected to the antenna conductor 3 as by means of a conductor 412 and the other terminal of the primary Winding 4|- being grounded as at 43. The cathode of the rectier 31 is preferably grounded as at 44 and connected to the other end of the transformer secondary Winding 39 through a load resistance 45 as by means of conductors 46 and 33, the cathode ends of the windings 3l! and 39 beingr interconnected and both being connected to the conductor 33 as is illustrated 'in Fig. 1.

The radio frequency component of the rectifier current flowing in the circuit 33-46 is preferably shunted around the load resistance I45 by means of a by-'pass condenser 41 connected in parallel therewith.

It will be noted that the rectifier 31 operates to produce across the resistance 45 a directpotential which is exactly proportional to the voltage Y of the antenna feeding conductor 3 with respect to ground and that the polarity of such voltage is such that the conductor 46 is positive with respect to the conductor 33. Thus the direct potential which may be applied to the conductor 26` with respect to ground is equal to the difference in direct potentials produced across the resist ances 3| and 45.

It will also be appreciated that any change in the resistance of the antenna circuit will -result in a change in both the antenna current and the voltage of the antenna feeding conductor 3 with respect to ground. Furthermore, such voltage and current changes will be in the opposite direction; that is, an increase in antenna resistance will tend to reduce the antenna current and at the same time tend to increase the voltage of the conductor 3 with respect to ground.

The resistances 3| and 45 are preferably so adjusted that the voltages thereacross are equal when the resistance of the antenna circuit is adjusted to the desired value. Consequently, a subsequentchange in antenna resistance as, for eX- ample, a reduction in antenna resistance, will result in the application of a positive direct potential to the conductor 26. This will cause current to ow through the relay coil 23 in one direction and so energize the motor i2 as to insert resistan'ce in the antenna circuit, by means of the variable resistance 9 to thereby compensate for the reduction in antenna resistance due to other extraneous causes.

Similarly, if the antenna resistance were to increase. the voltage produced on the conductor 26 would be negative with respect to ground and current would flow through the relay coil 23 in the opposite direction so as to oppositely energize the motor I2 and result in resistance being ret moved from the antenna circuit at the variable resistance 9, Thus, the control mechanism21 costant irrespective of any other electric changes or physical changes tending to change the net electrical resistance of the antenna circuit.

In a similar manner I' have arranged for the controll of the variable inductance I0 in such manner as to maintain the inductance or inductive reactance of the antenna constant irre,v spective of physical changes tending to shift thereactance of antenna circuit from the desired operating value. The Variable inductance l0 is, therefore. arranged to be varied by the rotation of a reversible electric motor 48 which is con-l nected to a suitable source of power 49 and arranged to be controlled in its direction of rotation by a polarized relay 50, the motor 48 and relay 5|) being connected in a manner identical to that previously described in connection with the motor i |2 and relay 22.

The control voltage for operating the polarized relay 50 is obtained from a conductor 5| which is connected to one terminal of the coil of the relay 50, the other terminal thereof being grounded as at 52. The control Voltage is supplied to the conductor 5I by means cfa control mechanism in'-v dicated generally in Fig. 1 by the reference character 53. This mechanism may include a potential transformer 54 including a primary winding 515 connected across the antenna feeding circuit as by connecting one terminal thereof to the antenna feeding 'conductor as by means of a conductor 56 and by connecting the other terminal thereof to ground as by means of a conductor 51. includes a secondary winding 58, one terminal of which is connected as by means of'a conductor 59 to the anode of a rectifier 66 and the other terminal of The potential transformer 54 which is connected as by means of a conductor 6| to the anode of a rectifier 62. the rectifier 60 is connected to the conductor 5l and is also interconnected with the cathode of the rectifier 62 through a pair of series connected resistances 63 and 64. The point of interconnection 65 common to both of the resistances 63 andv and 62 are shunted around the resistances 63 and B4 by means of bypass condensers 63 and 10 and any stray radio frequency Voltages'appearing on the conductor 5| are preferably by-passed to ground .by means of'a condenser 1|.

The above described circuit operates to apply across the rectifier Gll a, voltage which is equal tothe vector sum of the voltage induced in the current transformerwinding 61 (directly proportional to thel magnitude of the current flowing in the antenna circuit) and one-half of the voltage induced in the potential transformer secondary winding 58. There is also applied across the rectifier 62 a voltage which is equal to the'vector sum of the voltage induced in the current transformer secondary winding 61 and one-half of the voltage induced in the potential transformer secondary winding 58, this latter voltage being, hoW- ever, out of phase with respect to the correphase of'voltage-across the winding 61 should The cathode of saliente normally-be; imphaseequadrature td fthatracros f.

Winding 58. A Vslight deviation' in. phase ``may :be compensa-ted byk adjusting the e mid-tap portion-1:: owindingin o As a result of-this: arrangement',:,theziratio of the voltagesv which are :appliedf to daherrectiersy land iv62oaref independent vof* the-factual magni tudezof the current owingin'the antenna circuit.` andare also independent of` theI actualy magnitude a respect-to gro-undi- However, rany changes Iin Athe phase;relation'between` the: antenna voltage `and Y the; antenna. .current vWi-llresultV in afi/change in z antes -Ei' and l Eril: are in opposite directions so that v theivol-tage-of the conductorY 5| withlrespect'togroundv-is equal to the diierence=between thevoltages :producedfacross the` resistancesaty dmThus; when the antenna exl'iibits-tlie desired inductive reactance; no voltage Will be applied to they-conductorolr and thezfrelay. 50' Will maintain a neutral'positionl so as to keep the control motor. 4B=k de-energizedu- IL1- howeverznthel reactance :oft theV antenna 'Y changes a-s a result, 4for example, of ya change;inactual: lengthV of; the antenna, l:there Iwill be produced -onfthe conductorSIza corresponding voltn age. This Will lcausethe'rnotor 48 t0 be energized tQ'rotate-,in such:A direction as to Vary the variableinductance I Il in a direction'opposite to the change` f in inductive reactan-ce yof the vantenna landv thus restore the-inductive rea'ctance `of-tl1e1anten'na-A circuitto the desired'value.

n W111- thus be noted that. the variable resiste ance 9, rtogetlrierfwith itspcontrcl'fand operating mechanism; and` the Ivariable inductance il` 'co' operatewith each other to maintainfthe electricaln eharacteristiczofther antenna- :I absolutelyY cone stant irrespectiveof other electrical'or extraneous.

Physical achangcs tending.` zto normally -vary the"7 antenna operating conditions from their desiredvalues-.1:1

I have illustratedsinFig. 2 a modified-form@ of. controlf' apparatus;intended-to` accomplish Athe same ultimate result offmaintaining the antenna "1. operating conditions 'substantially.constant.' I

have;..therefore,'illustrated inFign 2 anA antenna:

Hlllfas-being connected` through a primary Windingl |(I'Ifnf-a-currenttran-sformer |02 to theoutVv put of a -suitable radio frequency power amplifier represented diagramrnatically` by the'- rectangle !`IJ3,-.^i,t being understoodthat the radio'frequency l power amplifier thus represented mayggbeof any suitable or' conventional-construction'f The otherA output terminal of the amplienlis connected tn ground by means of a conductor I E14-through a .primary --WindingH-I `of-a current-1y transf former |06.'-

The-radio `frequency amplifier ||l3wis arranged towbefexcited by -a `su-itablefsource` ofliradio' fre fluency voltage conveyed tothe locationwoftheamplien- Iflbyfmeans cfa-a suitable-transmission l line |01 illustrated in rFig; s2 as compri-sing a -ooaxial-cablefincludin-gV a central conductor I 08 #andv closed within-and insulatedwfrom; a AfgroundedwA metallicV sheath I B9; Thefftransmission-line l I iszunderstoodfto beconnectedto Aa suitable sourcere of radioffrequency voltage @diashow-nl,y Which/f. Sourcen-may tbe of y'any suitable-wor `conventional=f construction. v

The conductor-..- D3i fis. coupledl by; means cof'ra blocking condenser-'I 09` and conductord In to ithe.` gridofA a gainlcontrolledlamplifying tube I Lfthevi outputfofwhi-ch'is connected as -byzmean-s` of. a conductor I'I2 to a Coupling .transformer I |13. The;-couplingtransformer H3 is connected|by m'eanslof' conductors ||4 ancl-` I |=5 tol theinput of: the-poweramplier. H13.:Y i r,

The system Whichfis illustrated"ir1;lig.^;.Zin-;1.` cludesA a `currentregulating means: for maintain?"L king the current flowing 'in' therantennaillratfa substantially "constant value f'irrespectiveiof: rex-w traneous .'changes' Vtending normallyz to .f cau-se; variation in the antenacurrent'. 1 regulatingf; equipment is indicated in Fig. 2 generallybyathe i: reference vcharacter IIiandfincludesfafrectier I Irlgthe anode of Vwhich :isconnected fby means" of;` a conductor IIS Fito. aseconda'ry Windingrl I9 -ofzthe@ currentistransforrner 1&2.' 'Then'secondary'fl winding. I'I'B is preferably `tuned' asl by'a variable condenser Iwto the-frequency lof the currentr` flowing in :thelantenna 00:1'

The cathode-of the vrectifier |I`|r isy connectedis to` the :other terminal `of xthe tsecondary'fwinding I iSv-by' means of a series circuitrinclud-ing. a coni-'f duister' |2I',"a bias battery=|2l2', conductorrIZSp load resistance |24, and conductor |2'5 The radio@` frequency component of the current flowing'm tlieabovey described series circuit? may be'rshunt'e'd around the battery |22. and the loadlresistamcei4 |21?. byi-means of l a condenser' |26" connectedbe-"A tween the 4conductors I2| and |25.'

The polarity ofthe battery |22.'1is arrangedf to apply Ya positive potentialto` the cathode'of@ the rectifier 1| I1 relative to' the anode! thereof so@ that the rectifier IVI will not be operative until f the peak voltage of the radiorfrequ'ency induced in the secondary WindingIIS exceedsithe'directf bias potential applied by the battery |225: When this .potential is exceeded, ra .direct current will fiow'through the load resistance |.24-to' produce;y a direct: potential drop thereacross in such fdirec'AIV t'io'nvasy to make the Voltage ofA the. conductor. |25 negative withrrespectto therconductor'123.

The conductor` l|23 'is preferablywgrounded as 'indicated-'at |21 so that the potentialpd the-V conductor |25- is forcedv furthernegative with respectl to ground with increases in current in` the antenna'circuit. The negative voltage ap-'a plied to the'ccnductor l'25'xispreferably` conveyed through'coupling resistances: `|28 and |29 and a conductor :|30 to the Ygrid of thev amplifyingltube s ||r|. The point of common connectionl between the Yresistances I 28 vand |29 is preferablyicon`` nected to ground through a by-pass'condenser I'SIThis 4byv-pass lcondenser coactsuvvith` .theyY couplingresistances-|l28 and I29to` prevent-any of the `radio `frequency voltages inducedf in the` secondary H91 from being applied to thegrid of i thegamplifying tube-.III The cathode of the 'tube III. is `,connected to ground throughva f potential, the amplication of the tube is at its maximum value so that there is applied to the input of the power amplifier |03 a maximum exciting potential. This is ordinarily adjusted to produce an output antenna current which exceeds the intended operating antenna current. This excess current will result in operation of the rectifier I |1 and the production of a control voltage across the load resistance |24 causing the conductor |25 to bear a negative potential with respect to ground. p

This negative potential is applied to the grid of the tube through the reslstances |28 and |29 and conductor |30 so as to increase the negative grid bias of the amplifying tube and so reduce the amplification thereof. This in turn reduces the magnitude of the exciting voltage for the power amplier |03 and tends to reduce the antenna current.

This system will thus establish a normal operating condition in which the grid of the tu-be I|| is maintained at a potential somewhat negative with respect to ground. Thus, if for any reason the current in the antenna increases, thevnegative bias on the tube will likewise increase to reduce the amplification of the tube and reduce the exciting voltage applied to the amplier |03 so as to thus reduce the current flowing in the antenna |00 back to the original intended value. v

The operation in case of a decrease in antenna current is, of course, the reverse. Such a decrease will result in the grid of the amplifying tube being shifted less negative with respect to ground to thereby increase its amplification and increase the exciting voltage applied to the power` amplier |03 so as to tend to increase the current flowing in the antenna |00 to its original intended value. y

Since the regulating equipment ||6 operates to maintain a substantially constant antenna current, the equivalent resistance and inductive reactance of the antenna circuit may be maintained constant by maintaining a fixed phase relation between the current flowing in the antenna and the exciting voltage which is applied to the grid of the amplifying tube I have illustrated in Fig. 2 generally by the reference character |34 a form of control apparatus which is capable of maintaining this desired phase relation. Generally speaking this mechanism includes a means for comparing the phase of the current owing in the antenna circuit with the voltage which feeds the amplifier I to produce a control voltage which is in turn used to -vary a variable reactance in such direction as to shift the reactance of the antenna rcircuit in a Idirection to restore the original desired phase relation. Accordingly I connect a primary Winding |35 of a potential transformer |36 between the transmission line'conductor |08 and ground. The transformer |36 includes a secondary |31 which may be tuned to the transmission frequency as by means of a condenser |38. The voltage produced across the winding |31 is amplified by a conventional amplifier circuit including a vacuum tube |39 and applied across the primary winding of a coupling transformer |40.

The transformer |40 includes a center tapped secondary winding |4|, the end connections of which are, respectively, connected by conductors |42 and |43 to the anodes of a pair of rectiers |44 and |45. The cathode of the rectifier I|44 is connected by means of a conductor |46 to' a duced across the winding |4|.

vl1,0 load resistance |41 and, similarly, tli cathode of the rectifier |45 is connected as -by vmeansiofa conductor |48 to a load resistance |49. f

The l-oad resistances |41 and |49 are connected together and their point of common connectionis returned to the center tap ofthe transformer winding |4| by means of conductors|55 Aand 7|;5I. `Conductors |50 and |5| connect, respectively, to voutput termin-als |52 and |53 of a phase shifting device |54. The phase shifting device |54 'infcludes also input terminals |55 and |56 connected, respectively, by conductors |51 and |53 to a secondary winding |59 of the previously mentioned current transformer |06.

The phase shifting device |54 comprises an adjustable mechanism operating to produce `across kthe output termin-als |52 and |53 a voltage which is equal to -or at least proportional to the voltage which is applied to the input terminals |55 and |55 thereof and permitting the time phase of the Ioutput voltage to be adjusted relative to 'the time phase ofthe input voltage.

It will, therefore, be noted that the rectifier |44 is included in a closed circuit in series relationship with .the upper half of the transformer winding |4|, lthe phase shifter |54 and the current 'transformer winding |59 and the load resistance |41. Similarly, the rectifier |45 is included in a closed circuit in series relationship with the lower half of the transformer winding |4|, the phase shifting device |54 and the current transformer secondary winding |59 and the load resistance |49. y p

The phase shifting device is norm-ally adj-usted to introduce into the two rectifier circuits between Ithe center ltap of the winding |4| and the cornmon connection between the resistances |41 and |49 a voltage which is proportional to the current flowing in the antenna |00 andwh'lch bears a phase quadrature rel-ation to the voltage in- Also the resistances |41 and |49 are preferably made equal-.so that .the direct potential produced across these resis'tances by the rectification-of the radio frequency volta-ge applied to the rectifiers |44 and |45 Will be equal.

Since the current ows through the resistances |41 and |49 in opposite directions, the conductor |46 will normally be at the same potential as the conductor |48.,r Should -a shift in phasel occur as above noted, the voltage applied to one or" the rectifiers would shift in one direction, whereas, the voltage applied to the other rectifierA would shift in the opposite direc-tion so .that the-voltages produced across the resistances |41 land |49 would no longer be equalwthereby producing a voltage between the conductors |46 and |48.

The conductor |48 is preferably groundedas indicated at |60 and the conduct-or |46 is preferably connected as by means of a conductor |6-| through resistances |62 and |63 .to the grid of a vacuum tube |34.

Undesired radio frequency may be filtered out of the above described control circuit by connecting Joy-pass condensers |65 and |66 in parallel, respectively, with the resistance-s |41 and |49 and by also connecting the point of comm-on connection between the resistances |62 and |163 .to ground through a by-pass condenser |61.

The cathode ofthe tube |64 is connected-to ground through a cathode bias resistance |68 which is preferably -shunted with a by-pass condenser |6'9. The plate of the tube |64 is preferably connected to the plat-e of the previously mentioned amplifier tube by means of a conductor |10 and is also connecte-d to thegrid` of the tube |84. through a coupling condenser ill.

Whenever the desired phase relationship exists between the .antenna current and the volta-ge dcm livered by the transmission line I?, the con-ductor IEl will be at ground potenti-al as .above noted and the grid bias applied to the tube |60 will be 'that which is developed by the cathode bias resistance Hi8. If lthis phase relation shifts from the desired relation, then the conductor |6| will have applied thereto a direct potential, the polarity of which with respect to ground is indicative of thedirection in which the phase shift has taken place and the magnitude of which is proportional to that phase shift. This will serve to increase or decrease the n-egativegrid bias applied to the tube |56 and will consequently correspondingly vary the mutual conductance of the tube.

The plate circuit for the vtube Hifi includes the vconductor |10, the cathode of the tube and the byfr pass condenser i093 so that radio frequency current is caused to ilow through this plate circuit and the tube, therefore, lcomprises an impedance which may .be 4considered .to oe connected in parallel with the'primary of the input coupling transformer H3 and the power amplier |03. This impedance varies with the vari-ations in grid bias of the tu'be |60.

The impedance provided by the plate circuit of the tube. |62 comprises an inductive reactance sincethe radio frequency voltage which is applied 'to .the grid of the tube |64 is derived from the conductor |10 and passed through the c-ondenser l|"H with the result that lthe radio frequency grid voltage of the tube bears a phase quadrature K relation to the voltage which is applied to the plate through the conductor |10.

Since the current drawn by the plate of the tube |04 must vary in accordance with the variations in the grid voltage of the tube, it will be:`

seen that-the radio frequency current which flows from the plate to the cathode of the tube |60 will be in phase quadrature relation to the radio frequency voltage existing between the plate and the cathode of the tube. Thus changing the amplification of the tube I produces a result equivalent to changing the inductancefor the capacitance of the tuned circuit Acomprising the primary of the coupling transformer H3. This will, of course, produce a phase shift and the various instrumentalitics hereinbefore described are so arranged that the phase shift thus produced is in a direction to compensate for the phase shift in the antenna current which resulted in the changing of the reactance comprising the plate circuit of the tube |60.

It will thus be seen that the control mechanism referred to generally by the reference character |34 operates to maintain a fixed phase relation between the current actually owing in the antenna |00 and the exciting voltage delivered by the radio frequency transmission line |01.

' As before noted, the regulating equipment indicated generally by the reference character IIB operates to maintain the current ilowing in the antenna at a constant value. Thus the antenna circuit must exhibit a constant resistance and reactance characteristic so that the time phase of the radio frequency potentials radiated into space must remain constant irrespectivel of physical or extraneous electrical changes tending to cause a shift in phase of such radiated energy.

I have illustrated diagrammatically in Fig.` 3 an arrangement whereby the required phase relationship .between two separate signalsemanating fromv a pair of radio beacon transmitting antennae may be so maintained as to cause the radio beacon course defined by the operation of the system to remain in a fixed compass direction irrespective of external changes ordinarily tending to cause a shift in the compass direction of the defined course;

As is illustrated in Fig. 3 a pair of radiofrequency transmitting antennae A and B' are spaced apart a predetermined distance and the signals emanating from the antennae A and B are so synchronized and phased with each other as to define atleast one radio beacon course identified by the solid line 200 in Fig. 3. As previously noted, the course 200 may comprise an equisignal course defined by a conventional equisignal radio beaconsystem or a system operating in accordance with the disclosure contained in my previously led copending application Serial No. 432,948,`led March 2, 1942, now -Patent No. 2,406,396, granted'August 27, 1946. On the other hand, the course 200 may comprise an equiphase difference course such as is defined by the new type of radio beacon system disclosed in my previously led copending application Serial No. 420,059,v led November 22,1941,` now abandoned.

lin either event I employe radio receiving apparatus R of a type'adapted to properly coopcrate with the type of radiofbeacon transmission which is emanated from the antennae A and B. The receiver -Ris positioned at a point 20| such that a line 202 drawn from the point 20| through the center or origin 203 of the eld pattern produced by the radio beacon system will comprise an extension of the course 200 or, in other words, will lie in the same compass direction as the desired Vand intended direction of the course 200. The receiver R is coupled to control the operation of the antennae A and B in such manner as to maintain the defined course 200 extended in the desired compass direction.

I have illustrated in Fig. 4 lthe arrangement which may be employed when the system illustrated in Fig. 3 comprises an equi-signal system. As is shown in Fig. 4 the antennae A and B are each energized from suitable power amplifiers represented bythe' rectangles bearing the reference characters 20^and 205. These amplifiers may be of any suitable conventional construction and `may also include such frequency doubling stages as may be desired to produce the desired ultimate frequency of radiation.

The amplifiers 204 and 205 are each arranged to be excited by radio frequency energy developed in a suitable oscillator or signal source represented -by the rectangle bearing the reference character 206; The source 206 may be positioned geographically as desired and the energy may be conveyed from the source 206 to the ampliiiers 204 and 205 through A suitable radio frequency transmission systems 201 and 208 illustrated diagrammatically in Fig. 4 as comprising coaxial cables of conventional construction.

The outlying end of the cable 20'! is preferably coupled directly to the input of the amplier 204 as by means of a coupling resistance 209. The outlying end of the cable 208 is, however, connected to a conductor 2|0 which is in turn connected to ground through two parallel circuits, one of which includes a potentiometer 2| I and a 'fixed inductance 2| 2 connected in series relationwith each other.

defined by the operation ofthe radio-beacon'system and a voltage of opposite polarity when the receiver R is positioned to the right of the defined course.

. For a more detailed description of the construc- `tion of the mechanism indicated by the rectangle 255 reference may be had to my copending application'Serial No. 424,159, led'December 23, 1941, wherein 'I have illustrated, described and claimed two dierent types of mechanisms which may be employed for this purpose. Also reference may be had to my copending application Serial No. 432,948, filed March 2, 1942, now Patent No. 2,404,811), granted July 30, 1946, wherein I have illustrated, described and claimed a, third form of apparatus which may be used for this purpose.

From the foregoing it will be noted that when the receiver R is positioned `alongr the line 222 and the antennae A and B areso excited as to define an equi-signal course extending along the line 202, the movable control element 25| will occupy an intermediate position and the control Ymotor 242 will be cie-energized.

In the event some change in conditions occurs such as a change in temperature serving to change the actual length of one of the antennae, the resulting phase shift of the signal emanated from the other will cause the equi-signal course dened by the operation of the system to swing to one side or the other of the line 202 in Fig. 3. This will serve then to position the receiver R to one side of the defined course with the result that a voltage will be'applied to the coils 251, the movable'element 25! will be moved into engagement with one of the contacts 249 or 258 and the motor 242 will be energized. This Will move the movable .condenser 235i and shift the phase of the signals emanating from the antennae A and B with respect to each other and the mechanism is so arranged that the direction of this phase shift will be in a direction opposite to that caused by the changing ex raucous conditions, with the result that the course dened by the operation of the system is shifted back toward its original position, andwhen the reshifted position of the defined .Course coincides with the lines 28B and 252, the voltage developed across the coils 25'! will be restored to zero and the motor 242 will be dc-energized.

Thus it will be seen that the control receiver R l coa-cts with the motorized phase shifting equipment to maintain the course dened by the operation of the radio beacon system extended a desired compass direction irrespective of disturbing influences or extraneous conditions tending to cause a shift of the defined course to a diierent compass direction.

I have illustrated in Fig. an arrangement similar to that described above in connection with Fig. 4 but adapted particularly for use with an equi-phase difference type of radio beacon system such as that described in my copending application Serial No. 420,059, filed November 22,

It will be noted by having reference to Figs. 4 and 5 that the transmitting equipment illustrated in Fig. 5 is identical with that illustrated `in Fig. 4 with the exception that the keying arrangement illustrated in Fig. 4 and required for equi-signal type of operation is omitted from the equipment illustrated in Fig. 5. It will be understood, of course, that in Fig. 5 the frequency multiplying stages employed in the power amplifiers 254 and 205 are different in number so that `the signal emanated from the antenna A is dif- I6 ferent` from that which is emanated from-the antenna B but bearing a harmonic relation thereto.

The system` illustrated in Fig. 5` also differs from thatwhich is illustrated in Fig. 4 as regards the receiving apparatus employed. In Fig. 5 the rectangle 253 is intended to represent a double channel radio receiver including two separate receiving channels, one tuned to the frequency emanated from the antenna A and' the other tunedto the frequency emanated from the an'- tenna B. Similarly. the equipment included within the rectangle 255 diiers from thatillustrat'- ed in Fig. 4 in that it comprises a phase discriminating apparatus operating to produce across the conductors 256 zero voltage when the phase relation between the signals received from antennae A and B bear a predetermined multiple phase relation to each other and operating to produce a voltage across the conductors 256 Whenever the phase relation departs from this predetermined phase relation.

The equipment is so arranged that the polarity of the voltage developed across the conductors 256 is directly indicative of the direction of phase shift. While any known type of phase discriminating apparatus capable. of producing this type of operation may be employed, preference is expressed for the apparatus which I have illustrated, described and claimed in my copending application Serial No. 420,059.

Thus the equipment which is illustrated in Fig. 5 operates in the same manner as that previously described in Fig. 4; a change in compass f' direction of the course resulting in the application of a correction to the transmitting equipment so asto shift the phase of theantennaA with respect to antenna B in such direction as to cause the course defined by the operation of the system to shift back to its original and `intended direction.

From the foregoing` it will be observed that I 'have Vprovided a novel apparatus for maintaining the course which is dened by a-radio beacon system extended in the desired compass direction. In other words, the apparatus of my invention operates automatically to eliminate the wavering or shifting of the defined course which now characterizes the radio beacony course-denning systems in present day use.

It will also be noted that I have provided for accomplishing this result in a number of Ways. In Figs. 1 and 2 I have disclosed apparatus which operates to accomplish this result by so regulating the operation of the radio beacon transmitting antennae as to Amaintain a fixed phase relation between the signals emanated from such antennae.

Figs. 4 and 5 represent a somewhat different approach to the problem wherein the phase relation between the two sets of signals ernanated from the beacon transmitting antennae is so controlled as to directly maintain the defined course extended in the desired compass direction irrespective of what the actual phase relation between the antennae may be.

Experiments have indicated that the use of apparatus of the character above described will result in reducing the undesiredr vshifting of the radio beacon course to as little as from two percentto `ten percent of the shift now encountered.

While I have shown and described the preferredembodiment of my invention, I do not desire to `be limited to any of thel details of construction shown or described herein, except as dened in the appended claims.

I claim:

l. In a radio frequency transmitting apparatus, the combination of: a source of radio frequency energy; a transmitting antenna having transmission resistance and reactance; a circuit coupling said antenna to said source; and a device for compensating for changes in said transmission resistance and reactance comprising a variable resistance in said circuit, actuating means operable to vary said resistance, control means responsive to changes in magnitude of antenna current, means coupling said control means to said actuating means for varying said resistance in accordance with changes in magnitude of said antenna current, a variable reactance in said circuity another actuating means operable to vary said reactance, another control means responsive to changes in phase of antenna current with respect to voltage of said circuit, and means coupling said other control means to said other actuating means for varying said reactance in accordance with changes in said phase.

2. In a radio frequency transmitting apparatus, the combination of: a source of radio frequency energy; a transmitting antenna having a transmission resistance; a circuit coupling said antenna to said source; and a device for compensating for ch-anges in said transmission resistance comprising a variable series resistance in said circuit, actuating means operable to vary said resistance, control means responsive to changes in magnitude of antenna current, and means coupling said control means to said actuating means for varying said resistance in accordance with said changes in magnitude of said antenna current.

3. In a radio frequency transmitting apparatus, the combination of: a source of radio frequency energy; a transmitting antenna having transmission resistance and reactance; a circuit coupling said antenna to said source; and a device for compensating for changes in said transmission resistance and reactance comprising a variable reactance in said circuit, actuating means operable to Vary said reactance, control means responsive to changes in phase of antenna current with respect to voltage of said circuit, means coupling said control means to said actuating means for varying said reactance in accordance with changes in said phase, and regulating lmeans for holding substantially constant the current owing in said antenna.

4. In a radio frequency transmitting apparatus, the combination of a source of radio frequency energy; a transmitting antenna having transmission resistance; a circuit coupling said antenna to said source; and a device for compensating for changes in said transmission resistance comprising a variable resistance in said circuit, actuating means operable to vary said resistance, measuring means coupled to said antenna for producing a potential proportional to the magnitude of the current flowing in said antenna, another measuring means coupled to said antenna for producing another potential proportional to the magnitude of the Voltage of said circuit, means for comparing said other potential with said rst-mentioned potential to 18 provide a control potential proportional to the difference between said other potential and said iirst-mentioned potential, and control means responsive to changes in said control potential for operating said actuating means.

5. The method of compensating va circuit including a variable reactance and interconnecting an antenna having transmission resistance and reactance with a source of radio frequency energy to correct for changes in said transmission resistance and reactance which consists in holding the current in said antenna substantially constant, and employing variations in phase relations between the voltage of said circuit and said current to vary said variable reactance.

6. The method of compensating a circuit including a variable series resistance and a Variable reactance and interconnecting an antenna having transmission resistance and reactance with a source of radio frequency energy to correct for changes in said transmission resistance and reactance which consists in employing variations in voltage of said circuit and variations of antenna current to vary said series resistance, and employing variations in phase relation between said current and said Voltage to vary said reactance.

7. The method of compensating a circuit including a variable series resistance and interconnecting an antenna having transmission resistance with a source of radio frequency energy to correct for changes in said transmission resistance which includes the step of employing variations in antenna current to vary said series resistance.

WILLIAM J. OBRIEN.

REFERENCES CITED The following references are of record in the le of this patent:

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